[Nicolas06]

I like my DA15, but there seems to be a cult there. It might be softer on corners but it should be good enough closed down... Isn't it?

Well I find it really depend on the subject/photo.My impression is the focal plan is curved more like a sphere so if you take a wall, the border are out of focus... because the focus is put not on the wall but on a sphere from witch the camera is the center.

I tend to see that if you are in front of this wall, or on this wall, think are not great but kind of ok. But if for any reason while you should have focus up to infinite (hyperfocal distance is only 1.5m at f/8), if the borders are futher away than the center you get quite soft borders.

Let see an example. First serie of attachements are the full picture (uncropped, uncorrected), a center crop and a border crop... Settings are DA15, f/8, iso 100, 1/400s.




And now second example, the border are not that much futher away; It also seems to me my copy is softer on the right corner but overall this is already far better.






Last example, the center is futher away and both borders are more not as distant. All borders are better. Right corner tend to be a little too soft, I wonder if I need my lens to be serviced.

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Last edited by Nicolas06; 12-21-2014 at 03:25 PM.

[Nicolas06]

What do you think ? How do you manage field curvature with your DA15? It seems to it apply most when border are futher away than center... And this tend to happen quite a lot in architecture shoots !

Also do you think the right border is weak enough it should be serviced ?

[manntax]

Not sure if it all can be justified by field curvature, especially with lens stopped down to F8 or past that there shouldn't really be ANY softness with that wide lens. My old tokina does 5 times better than your samples provided here. The problem with your lens might be the focusing. Even my lens when focused manually in live view can give soft appearance to some parts of the shot while even little change in focus makes the whole scene tack sharp . If you use autofocus for shooting you could do better with manual focusing imo since I found pentax AF to be extremely unreliable - especially with very wide lenses.

[enoeske]

I like my DA15, but there seems to be a cult there. It might be softer on corners but it should be good enough closed down... Isn't it?

Well I find it really depend on the subject/photo.My impression is the focal plan is curved more like a sphere so if you take a wall, the border are out of focus... because the focus is put not on the wall but on a sphere from witch the camera is the center.

I tend to see that if you are in front of this wall, or on this wall, think are not great but kind of ok. But if for any reason while you should have focus up to infinite (hyperfocal distance is only 1.5m at f/8), if the borders are futher away than the center you get quite soft borders.

Let see an example. First serie of attachements are the full picture (uncropped, uncorrected), a center crop and a border crop... Settings are DA15, f/8, iso 100, 1/400s.




And now second example, the border are not that much futher away; It also seems to me my copy is softer on the right corner but overall this is already far better.






Last example, the center is futher away and both borders are more not as distant. All borders are better. Right corner tend to be a little too soft, I wonder if I need my lens to be serviced.

I would send it in for servicing (or return it if possible). Looks like you've got a decentered lens element.

[Mikesul]

Do any wide angle lenses avoid edge problems completely? Always some kind of trade off - size for instance.

[kh1234567890]

There is something wrong with most DA15's. And it is not field curvature

[enoeske]

There is something wrong with most DA15's. And it is not field curvature

most? 2 problems does not constitute most.

[Dartmoor Dave]

There is something wrong with most DA15's. And it is not field curvature

NEWSFLASH: Legion of the mind-controlled spotted heading towards Manchester, carrying pitchforks and blazing torches and chanting, "KILL THE HERETIC!"

Fortunately it will take them several months to reach you, because every time they walk past a tree they have to stop to take an HDR shot of sunstars through the leaves.

[Rondec]

I think de centering is actually pretty common with this lens. I need to send my copy in for servicing. I think it used to be OK and now, if it isn't focused to infinity and stopped down, the right side is pretty poor. It is just a tough lens to send away for a vacation because I enjoy shooting with it a lot...

[Nicolas06]

I think de centering is actually pretty common with this lens. I need to send my copy in for servicing. I think it used to be OK and now, if it isn't focused to infinity and stopped down, the right side is pretty poor. It is just a tough lens to send away for a vacation because I enjoy shooting with it a lot...

Yeah apparently I'd need servicing

[Nicolas06]

So after quite some time I sent the lense for servicing...

Pentax ask for 125€ to "calibrate the lense on adjustment bench". Not sure it is perfect traduction for the french "pour un étalonnage sur le banc d'ajustement.".

I'am just asking because I don't know at all in general how lense repear work... Would it fix the issue ? As for price, it look ok if it fix the issue, but I'd like to be sure.

Any throughts?

[kh1234567890]

Any throughts?

It will come back bad but in a subtly different way. You should have marked the front trim so that you could tell if they've actually opened it rather than just leave it sitting on a shelf somewhere for a while. No-one knows what criteria Pentax use to pass/fail a lens. The price seems about right if they fix the problem.

[Nicolas06]

So it came back and I can't say I'am happy with the result.

With AF, there still the issue that the right part of the lense is very soft.

An example with a subject at maybe 3-4meter of distance. f/8 apperture. If I use MF and focus on infinite the right part is sharp, but center and left is not. If I focus at 1meter (hyperfocal at f/8 is 0.95 , everything should be in focus till infinite) then the center is sharp but the right part is very soft.

Putting the focus in the middle still doesn't give me a picture that is reasonably sharp everywhere. I don't ask for perfect sharpness, but I'd like something that look perfectly sharp say in FullHD, fullscreen.

In attachement, in order:
- center infinite focus
- right border infinite focus
- center 1meter focus
- right border 1meter focus

I already paid 125€ for the last work on the lense and it look like it didn't bring anything. I'am confused about what I should do? Buy a new DA15 lense and consider this one as broken? Consider that the DA15 doesn't suit me and look for another model? Unfortunately, I don't know alternative small/light UWA lenses primes...

[kh1234567890]

Told you so. The 'acceptance' criterion test probably involves shining a torch in at one end and checking that the light comes out at the other. Send it back (or sell it on eBay and hide).

Is there any wobble on the lens barrel ?

[tibbitts]

Probably the entire industry is facing this problem: what standards to apply to lenses. When you have as many megapixels as we have today and you can test at very low cost, you're going to test, and find problems where you might not have before. So what was an acceptable lens at 6mp may now be unacceptable/defective at 24mp.

It seems like we've had some cases reported where problems like decentering were fixed by repair, and some where they were made worse, and some where no change occurred. I know in my case I wasn't able to get my issue resolved, although that was with another manufacturer, not Pentax. We just didn't agree on what was acceptable or how to measure - their corners/edges weren't my corners/edges, and they were testing at lower mp than what was commonly available at the time. So maybe in this case Pentax was testing with some old 1mp test equipment or something, and thought your lens was looking pretty good. They won't tell us, so we just don't know.

The wobble issue is another subject. I know I can get dramatically different results from my longer zooms by just letting gravity affect the front element in different ways - such as mounting the camera with the left or right side up on my ball head. The centers are always sharp, so it's not a matter of vibration or (center) focusing, but the edges are just completely different with different orientations. Then I can support the front section of the same lenses and get completely different results again - sometimes better, sometimes worse, and not always exactly repeatable.